1. Technical Field
The present invention relates to adjustment of the position of a lens used, for example, in a projector.
2. Related Art
In a projector, to adjust the position of a lens, such as a zoom lens and a focus lens, a transmission mechanism is used to transmit the power of a motor to a conversion mechanism formed, for example, of a rack and a pinion. The transmission mechanism is formed, for example, of gears, and the position of the lens can be detected with an encoder that detects the amount of rotation of any of the gears. In general, since such a transmission mechanism has what is called a backlash that is, for example, a gap between engaging portions of gears or engaging portions of a gear and a thread, the lens position detected with the encoder may deviate from the actual lens position. In view of the fact described above, a method for accurately adjusting the lens position by canceling such a backlash has been proposed. JP-A-2009-42621 discloses a method for moving a lens to a position registered in advance (hereinafter referred to as “registered position”) by first moving the lens in a predetermined direction, stopping the lens in a position beyond the registered position, and then rotating a motor backward to return the lens to the registered position. In the method, a backlash is eliminated by rotating the motor backward.
The amount of backlash changes due to environmental conditions (such as temperature and humidity) and elapsed time. In consideration of the fact described above, a method for returning a lens to an accurate registered position even when the amount of backlash changes has been proposed as follows: The method includes registering a final movement direction of the lens used when the position thereof is registered (hereinafter also referred to as “registration direction”) along with information on the registered position, moving the lens in the same direction as the registration direction when operation of moving the lens to the registered position (hereinafter referred to as “return operation”) is carried out, and placing the lens in the registered position. When the method is used in a state in which the registered position is close to an end point of the movable range of the lens, however, a user may feel something is wrong with user's fine adjustment of the lens position made after the lens is returned to the registered position.
Specifically, assume that the position registration is made by moving the lens in a direction toward one end point of the movable range of the lens (hereinafter referred to as “direction A”) and then moving the lens for the position registration in the opposite direction (hereinafter referred to as “direction B”) after the lens reaches the end point. To return the lens to the registered position, the same operation is performed and the lens is eventually moved in the direction B and reaches the registered position. When the registered position is close to the end point of the movable range, the user is likely to make a fine adjustment of the current lens position toward the end point after the lens reaches the registered position. When the fine adjustment of lens position is made this way, the movement direction of the lens (direction A) is opposite to the direction B, which is the final movement direction used to return the lens. In this case, the backlash present in the transmission mechanism is first eliminated, and then the lens starts moving toward the endpoint after the backlash is eliminated. As a result, there is a delay between the time when the user starts the fine adjustment of the lens position and the time when the lens position is actually changed, and the delay may disadvantageously cause the user to feel something is wrong.
The problems described above are not limited to a projector but common to an arbitrary apparatus having a lens and a mechanism that drives the lens. It has therefore been desired to develop a technology that cancels a backlash in a transmission mechanism for accurate movement of a lens and does not cause a user to feel something is wrong. In relation to a lens drive apparatus of related art, it has also been desired, for example, to reduce the size, lower the cost, save resources, simplify manufacturing processes, and to improve the degree of ease of use of the apparatus.